Medusas inmortales

La próxima vez que en la playa les pique una medusa, porfa no la maldigan demasiado. Son invertebrados interesantísimos de los que los científicos sacan mucho provecho. El motivo tiene que ver con la posibilidad que tienen de rejuvenecer. Algo que en el magnífico reportaje de N. Rich para el magazine del NYT se describe como un proceso hacia la inmortalidad. Vamos como si un pollo regresara al estado de huevo. Aquí he escogido algunos buenos motivos por los que las "sencillas" medusas resultan un banco de pruebas muy útil.

"Until recently, the notion that human beings might have anything of value to learn from a jellyfish would have been considered absurd. Your typical cnidarian does not, after all, appear to have much in common with a human being. It has no brains, for instance, nor a heart. It has a single orifice through which its food and waste pass — it eats, in other words, out of its own anus. But the Human Genome Project, completed in 2003, suggested otherwise. Though it had been estimated that our genome contained more than 100,000 protein-coding genes, it turned out that the number was closer to 21,000. This meant we had about the same number of genes as chickens, roundworms and fruit flies. In a separate study, published in 2005, cnidarians were found to have a much more complex genome than previously imagined.

“There’s a shocking amount of genetic similarity between jellyfish and human beings,” said Kevin J. Peterson, a molecular paleobiologist who contributed to that study, when I visited him at his Dartmouth office. From a genetic perspective, apart from the fact that we have two genome duplications, “we look like a damn jellyfish.”

This may have implications for medicine, particularly the fields of cancer research and longevity. Peterson is now studying microRNAs (commonly denoted as miRNA), tiny strands of genetic material that regulate gene expression. MiRNA act as an on-off switch for genes. When the switch is off, the cell remains in its primitive, undifferentiated state. When the switch turns on, a cell assumes its mature form: it can become a skin cell, for instance, or a tentacle cell. MiRNA also serve a crucial role in stem-cell research — they are the mechanism by which stem cells differentiate. Most cancers, we have recently learned, are marked by alterations in miRNA. Researchers even suspect that alterations in miRNA may be a cause of cancer. If you turn a cell’s miRNA “off,” the cell loses its identity and begins acting chaotically — it becomes, in other words, cancerous.

Hydrozoans provide an ideal opportunity to study the behavior of miRNA for two reasons. They are extremely simple organisms, and miRNA are crucial to their biological development. But because there are so few hydroid experts, our understanding of these species is staggeringly incomplete.

“Immortality might be much more common than we think,” Peterson said. “There are sponges out there that we know have been there for decades. Sea-urchin larvae are able to regenerate and continuously give rise to new adults.” He continued: “This might be a general feature of these animals. They never really die.”